Grav - The modern open source flat-file CMS
PHPmaker - PHPMaker is a powerful automation tool that can generate a full set of PHP quickly from MySQL, PostgreSQL, Oracle, Microsoft Access, Microsoft SQL Server and SQLite databases.
Bludit - Bludit is a web application to build your own website or blog in seconds, it's completely free and open source. Markdown support.
P4A - Php For Applications - PHP5 RAD Framework based on Zend Framework.
HTMLy - HTMLy is an open source databaseless blogging platform. A Flat-File Blog and Flat-File CMS written in PHP prioritizes simplicity and speed.
MT Backend - MT backend is a PHP control panel solution for websites.